1. Field of the Invention
The present invention relates to a heating unit and an image formation apparatus including the heating unit and in particular to a heating unit capable of reducing flicker and an image formation apparatus including the heating unit.
2. Background Art
Hitherto, a toner image fuser including heat generation means for generating heat in response to energization, a heating roller being heated by the heat generation means for fixing a toner image on a record medium, and energization means for intermittently energizing the heat generation means for adjusting the temperature of the heating roller has been designed. This kind of fuser is used with a copier, a laser printer, etc., for forming a toner image by electrophotography, for example, to heat and fix toner transferred onto a record medium such as paper from a photoconductor drum, etc. This kind of fuser can use a heater implemented as a halogen lamp, etc., for example, as heat generation means, and energization of the lamp can also be controlled through a triac, etc., so that the surface of the heating roller containing the lamp reaches any desired temperature.
However, a large current called rush current flows just after energization of the lamp is started. Thus, to use a copier, etc., using a power supply common to a lighting fixture in an office, etc., the power supply voltage of the lighting fixture lowers each time the rush current flows. If lowering of the voltage occurs at a frequency in the neighborhood of 8.8 Hz, human beings feel it as displeasing flicker of illumination light. In recent years, a large lamp of about 10 kw has been increasingly used as the lamp as the heat generation means; to suppress occurrence of flicker accompanying the rush current is an urgent problem. To solve this problem, to suppress occurrence of flicker, the following toner image fuser is known: When energization means executes energization, discontinuous energization is executed in a pulstile manner at the energization starting time, thereby dividing rush current into pulses and raising the voltage lowering frequency caused by the rush current for changing the strength of illumination light at a high frequency preventing human beings from feeling displeasure and well suppressing occurrence of flicker. (For example, refer to JP-A-11-095606)
As a method of generating such discontinuous pulses, energization means maybe provided with energization start time energization control means for discontinuously executing energization in a pulsatile manner at the energization start time, and the energization start time energization control means may be made up of energization control means for executing energization if a control signal is on when the voltage value of AC power supply crosses zero and stopping energization if the control signal is off when the voltage value of the AC power supply crosses zero and control signal generation means for turning on/off the control signal. As energization is thus started at the zero crossing time, the rush current can be reduced.